Today, ferroelectric thin films of BST and PZT as memory material of DRAMs, FRAMs and so on are being actively developed, and major concerns in such dielectric thin films are the fatigue characteristics and data-retention characteristics of the film.
Generally, with respect to a dielectric memory material, a platinum electrode is used as the electrode material of the ferroelectric thin film provided on the SiO2 on the substrate. Nevertheless, with this platinum electrode, due to its own catalytic effect, there are problems of hydrogen deterioration of ferroelectric thin films caused by hydrogen processing during the device process and fatigue deterioration resulting from the localization of oxygen deficiency toward the electrode side, and there is a problem in that the aforementioned characteristics cannot be sufficiently acquired.
Thus, as a substitute for such platinum electrode, there is growing interest in a Ru oxide sintered body. Electrode material obtainable from such Ru oxide sintered body (e.g., SrRuO3) has the potential of becoming a superior electrode material with bulk resistivity of 10−5Ω·m or less.
However, the Ru oxide sintered body; that is, an oxide having a perovskite structure represented with a chemical formula of MRuO3 (M: one or more types among Ca, Sr, Ba), is difficult to sinter, and the density obtainable with an ordinary pressureless sintering method is 70% or less.
Generally, sputtering is performed to a Ru oxide sintered body target to form a thin film. Nevertheless, when machine processing this type of low-density MRuO3 sintered body into a target, the yield becomes extremely inferior and the formation of particles upon sputtering with this target increases considerably. Thus, the formation of favorable thin films cannot be realized.
Therefore, even if the characteristics as an electrode material are superior, there is a major problem in that the uniformity and surface morphology of the film will become inferior when used as a thin film electrode.
Thus, although the sintering conditions are being devised with the perspective of high densification of the MRuO3, the current status is that a sufficient density is yet to be achieved. For example, although the pressure sintering method is effective in high densification, when using a graphite die generally employed in hot pressing, the intended MRuO3 sintered body cannot be obtained due to the reduction of MRuO3 caused by the reaction between the die and MRuO3. Moreover, there is another problem in that the consumption of the die is severe.
Meanwhile, in order to guarantee the operational performance as a reliable semiconductor, it is important to reduce as much as possible the impurities, which are detrimental to the semiconductor devices, in the aforementioned materials formed after sputtering.
In other words,                (1) Alkali metals such as Na, K;        (2) Radioactive elements such as U, Th; and        (3) Class elements of transition metals such as Fe, Ni, Co, Cr, Cu, Alshould be reduced as much as possible, and it is desirable that the purity be 4 N; that is, 99.99% (mass) or more. As used herein, every %, ppm and ppb represents mass %, mass ppm and mass ppb, respectively.        
Alkali metals such as Na, K, which are the aforementioned impurities, cause the deterioration of MOS-LSI surface characteristics since they easily move within the gate insulation film, radioactive elements such as U. Th cause the soft error of devices with the á ray emitted by such elements, and class elements of transition metals such as Fe, Ni, Co, Cr, Cu, Al contained as impurities are known to cause trouble in interface bonding.